This invention relates to power supply systems which furnish DC current at a certain voltage to electrical loads; and more particularly, it relates to such power supply systems in which the loads are segmented and the power supply system has redundancy.
Typical electrical loads for such power supplies are integrated circuits. They are usually packaged on printed circuit boards which have power and ground pins as well as multiple input/output pins for receiving and sending signals. Hundreds of these boards are often included in a single electronic system, such as a large data processing system or a large communications system. Multiple backplanes are commonly provided to hold the boards in groups of 10 to 20 and send signals between them, and each backplane has its own power and ground buses.
One way to provide power to such a multiple backplane system is to cable the power buses of all the backplanes together, and to connect them to a set of power supplies which operate in parallel to share in furnishing the total load current. Also, a redundant supply (i.e., an extra supply) can be included in such a system so that if any one power supply fails, the electronic system can still operate. This type of power supply system, including a redundant supply, is described in U.S. Pat. No. 4,698,738 by J. Miller and J. Walker which is assigned to the present assignee.
However, in a multiple backplane electronic system, it is often desirable to have the backplanes and their supplies segmented (electrically isolated) from each other. Such segmenting enables the supplies for just one backplane to be turned off while the supplies and the circuitry of the remaining backplanes continue to operate. For example, large data processing systems often contain multiple digital computers, each of which is housed on a different backplane. When the circuitry in one of those computers fails or needs to be upgraded, it is desirable to be able to power down just the backplane of that one computer so that the repair or upgrade can be made while at the same time, the remaining computers continue to operate. However, with the above referenced power supply system, this cannot be done because there, power cannot be independently applied to and removed from the individual backplanes.
One way to solve the above problem is to not connect the power buses of the backplanes together, and to provide a separate set of power supplies (such as those of the referenced power supply system) for each backplane. But in that case, a separate redundant supply would also have to be provided for each backplane; and that would substantially increase the cost of the system. For example, consider an electronic system of FIG. 1 which has three loads L.sub.1, L.sub.2, and L.sub.3. Suppose further that load L.sub.1 requires two power supplies 1A and 1B to furnish its load current; load L.sub.2 requires just one power supply 2A to furnish its load current; and load L.sub.3 requires three power supplies 3A, 3B, and 3C to furnish its load current. In that case, a total of six power supplies are required to furnish the needed load current, but an additional three redundant supplies R (one for each load) are also required to provide redundancy. Thus, redundancy increases the cost of the system by 50%.
Accordingly, it is a primary object of the invention to provide a power supply system in which all of the above problems are avoided.